Notwithstanding the Iowa administrative procedure Act, chapter 17A, any party, as defined in the rules and regulations promulgated by the board as provided in section 476.2, to a contested case before the board may within twenty days after the issuance of the final decision apply for a rehearing. The board shall either grant or refuse an application for rehearing within thirty days after the filing of the application, or may after giving the interested parties notice and opportunity to be heard and after consideration of all the facts, including those arising since the making of the order, abrogate or modify its order. A failure by the board to act upon the application for rehearing within the above period shall be deemed a refusal of the application. Neither the filing of an application for rehearing nor the granting of the application shall stay the effectiveness of an order unless the board so directs.